In isolated power converters it may be desirable to communicate signals from the secondary side to the primary side. Some types of communication may include synchronizing primary and secondary switch timing and communicating changes in load power demand. Some example techniques to communicate between the secondary and primary include a separate communication channel, which may require isolation, such as an optoisolator. Other examples may require additional components to modulate existing signals already occurring in the power converter, such as modulating a ringing frequency.